Tools for rapidly driving fasteners such as pins, brads, staples and the like are commonly used in the commercial work place. All of these tools have standard components comprising a housing, a driving element, a nose assembly defining a drive track in which the driving element can travel rectinearly, a power driving mechanism mounted within the housing to impart a forward or driving and a return stroke to the driving element, and a magazine in which the fasteners are stored and fed sequentially one at a time into the drive track.
Although all tool designs are based on the premise that the fastener aligns precisely in the drive track and each fastener in turn is driven perfectly into the workpiece, it does not always happen. Due to tolerances of both the fasteners and the tool components, there are times when the fastener is not seated properly in the drive track. If the misalignment is significant, the fastener may become jammed in the drive track rather than enter the workpiece.
Another malfunction is caused by the workpiece being hard or difficult to penetrate. The leg or shank of the fastener has a column strength defined by the material from which it is made. Should the resistance to penetrate the workpiece become greater than the strength of the fastener, then the leg may buckle and jam in the drive track. Debris, woodchips or the like may also cause a fastener to become jammed in its drive track and must be removed before the tool will again operate correctly.
Many various designs have been devised to provide access to the drive track in order to remove a jammed fastener. Commonly, such designs provide a drive track defined by a front plate attached to the housing and a back plate, which is formed from a part of the magazine assembly. When the magazine is held within the housing by a latch, the front and back plates abut to form the complete drive track. To have access to the drive track, the magazine latch is released and a portion of the magazine containing the back plate can be pulled backward away from the front plane. One example of such a fastener driving tool is shown in U.S. Pat. No. 5,054,678. Although the drive track of this tool is normally exposed, there is usually other fasteners still remaining in the magazine, which are next to the jammed fastener. Typically, all of the remaining fasteners must be removed from the magazine to allow proper access to remove the jammed fastener. After cleaning the drive track, the fasteners must be reloaded and the magazine closed and latched. Not only is this process time consuming, but the components to provide the latching and magazine movement are an added cost.
U.S. Pat. No. 3,273,777 discloses another nose assembly, in which a front portion of the nose assembly pivots outwardly to expose the drive track. Those skilled in the art will recognize the difficulty in designing a mechanism to securely hold the front plate in an operative position and yet easy to open, when a jam occurs. The front plate is held in an operative position by components creating a frictional latch. The front plate is automatically released to an inoperative position should the force against the front plate exceed the frictional latch. This design works well when a tool is new, but it is understood that after extended usage, the frictional forces of the latch components decrease, creating an undesirable tendency at times to open during normal fastener driving operation even though a jam did not occur. The worn or defective latch components must be replaced to again have the tool in proper working order. Any repairs needed on tools is both time consuming and costly.
Other fastener driving tools include a similar pivotal front plate and a latching mechanism, which use a manually releasable lever or cam to more securely hold its front plate. The disadvantage here is the cost of producing the necessary components.